1. Field of the Invention
The present invention relates to a sheet forming apparatus and a sheet forming method, and more particularly, to an apparatus and a method for forming resin coming out of a die into a sheet shape by using rolls.
2. Description of the Related Art
There has heretofore been known a sheet forming apparatus configured to sandwich resin coming out of a die between a first roll and a second roll and then to cause the resin to contact the second roll for a predetermined length in a circumferential direction of the second roll, the predetermine length being made variable by use of a third roll that revolves around the second roll. This technique is disclosed in Japanese Patent Application Laid-Open No. Hei 8-230018 (Patent Document 1), for example.
While each of the rolls has a function to cool down the resin coming out of the die, the predetermined length (a contact length of the resin with the second roll) is appropriately changed to prevent crystallization of the resin as well as to ensure transparency and homogeneity of the resin in the case where the resin is any of thermoplastic resins, in particular, olefin resins such as polypropylene or polyethylene.
Incidentally, the third roll of the conventional sheet forming apparatus is configured to revolve around the second roll while supported by a coupling member. However, this supporting style has a problem of degradation in positioning accuracy of the third roll when the resin is sandwiched between the second roll and the third roll with a high pressure.